FIG. 11 is a circuit diagram illustrating an example of a configuration of a switching power supply apparatus disclosed in JP 2005-137178A. In this switching power supply apparatus, an inverter 1 that includes an H-shaped bridge constituted by four switches converts a DC voltage Vin applied to input terminals T1, T2 that are provided at both ends of a capacitor 2 into an AC voltage. A resonant inductor 4 and a primary coil of a transformer 3 are connected in series to a bridging portion of the H-shaped bridge, and thus the AC voltage converted by the inverter 1 is transformed by the transformer 3, and the transformed AC voltage is rectified by a rectification circuit 5.
The rectification circuit 5 includes a diode 51 whose anode is connected to one terminal TA of secondary coils of the transformer 3, and a diode 52 whose anode is connected to another terminal TB of the secondary coils. Cathodes of the diodes 51, 52 are connected to each other. The rectification circuit 5 outputs the rectified DC voltage to a snubber circuit 6 from the cathodes of the diodes 51, 52 that are connected to each other.
In the snubber circuit 6, one terminal of a capacitor 61 is connected to the cathodes of the diodes 51, 52 that are connected to each other, and the other terminal of the capacitor 61 is connected to an anode of a diode 62 and to one terminal of a regenerative inductor 63. A cathode of the diode 62 and the other terminal of the regenerative inductor 63 are connected to the center tap between the secondary coils of the transformer 3.
The DC voltage in which surge voltages are absorbed and reduced by the snubber circuit 6 is smoothed by a smoothing circuit 7, and the smoothed DC voltage Vout is output from output terminals T3, T4. In the smoothing circuit 7, one terminal of an inductor 71 is connected to the one terminal of the capacitor 61 of the snubber circuit 6, and the other terminal of the inductor 71 is connected to the output terminal T3 and to one terminal of a capacitor 72. The other terminal of the capacitor 72 is connected to the output terminal T4 and the center tap between the secondary side coils of the transformer 3.
In the switching power supply apparatus having such a configuration, the capacitor 61 of the snubber circuit 6 and the resonant inductor 4 provided on the primary side of the transformer 3 constitute an LC serial resonance circuit, which enables suppression of a surge voltage that is applied to the diodes 51, 52 of the rectification circuit 5.